Answer:

Explanation:
By definition, the radius of a circle is the distance from its center to its edge.
We need to remember that diameter of a circle is twice the radius:

Then, you can observe in the figure that there are 4 units between the center of this circle and its edge, therefore the radius is:

Finally, you need to substitute the radius calculated into the formula
to find the value of the diameter of this circle. Then, this is:

